Five studies presented at the Alzheimer's Association conference in Boston on Wednesday found that people who were clinically healthy but anxious about memory lapses were significantly more likely to develop more severe problems in future.

The findings suggest that people should trust their instincts and consider seeking advice if they are concerned about memory lapses, while doctors should not dismiss patients' worries too readily, researchers said.

The studies focused on patients with "subjective cognitive decline", or self-reported problems with memory which are often dismissed as a normal consequence of ageing.

One group of researchers, from two US hospitals, found that elderly people with concerns about their memory but were otherwise deemed healthy had significantly greater levels of plaque which accumulates in the brains of Alzheimer's sufferers.

Pensioners who report changes in their memory are almost twice as likely to be diagnosed with dementia or mild cognitive impairment, a milder condition, within the next ten years, according to a separate study by University of Kentucky experts.

New guidelines are needed to define subjective cognitive decline and help doctors identify which patients may be at risk of developing more severe problems, researchers from the University of Bonn claimed.

"Recent data from several research groups have provided evidence that self-reported decline in cognitive performance in elderly people, even those with normal performance on cognitive tests, is a risk factor for future dementia and Alzheimer's disease, and may indicate an increased likelihood for the presence of preclinical Alzheimer's", they said.

Dr Marie Janson of Alzheimer’s Research UK said: "Self-reported memory problems could become an important tool for clinicians seeking to detect dementia early.

"While forgetting things occasionally happens to all of us, a serious worry about declining memory or thinking skills could be an early indicator that something else is going on. It’s a good idea for anyone with concerns to chat to their doctor."